March 15: Ides Of March Severe Weather Threat



Any time you can lead off a science/weather blog with a Shakespeare reference and a classical portrait of Roman history, it’s a good day.

Two rounds of rain in the forecast today…one moving through this morning, then some stronger storms late this afternoon and early this evening. It’s those late-day storms that will bring us the greatest severe weather threat — a borderline severe set-up, but something we’ll watch carefully all day.

This morning’s rain is falling apart as I’m typing this, and we’ll remain largely dry through mid-afternoon. It will be warm and breezy — strong southwesterly winds will push temperatures into the 70s:That level of warmth is sufficient for severe weather, but warm air is just ONE of the severe weather ingredients necessary to “cook up” a significant threat:While today’s humidity will definitely be noticeable, dew points will only reach the low 60s — that’s a borderline supply of moisture for severe thunderstorms:Also, the upper atmosphere isn’t all that cold compared to temperatures at ground level — that lack of cold air will act like a lid to suppress developing storms. If some storms manage to punch through that lid, there’s PLENTY of wind energy in the atmosphere. We’ll feel that wind energy all day, even in advance of the storms — gusts in the 20 to 30 mph range will be common:The storms will move in and move out quickly…unfortunately, it looks like the most-active time frame will be right around rush hour this evening. The HRRR model’s radar simulation from noon through midnight shows the progression of the showers and storms:I think that model has a reasonable depiction of what kind of activity we’ll see — numerous showers and storms, a couple of which could become severe. The Storm Prediction Center has included most of central North Carolina in a “Marginal Risk” (level 1 of 5) of severe weather:Damaging winds will be the primary threat, but there’s enough spin in the atmosphere that I can’t completely rule out the possibility of an isolated tornado or even some large hail:I wouldn’t be surprised if we’re eventually bumped up to a “Slight Risk” (the next level up the scale) in updated SPC outlooks later today. The SPC’s own forecast model shows a 70%-90% chance of favorable severe weather ingredients as the storms are moving in:Okay, but HOW favorable? That’s an important question! That same forecast model indicates a “Supercell Composite Parameter” (a statistic to quantify those ingredients) around 3. That’s elevated, but I’d be significantly more concerned if it was 6 or higher:In terms of our can’t-completely-rule-it-out tornado threat, that model’s estimate of the “Significant Tornado Parameter” shows a value around 1:Anything that isn’t zero gets our attention, but it could definitely be worse — STP values were in the 4-8 range earlier this week in Louisiana and Mississippi.

BOTTOM LINE: Don’t re-arrange your life around an outside chance of severe weather. Just stay weather-aware late this afternoon and early this evening, in case some warnings are issued. We’ll keep you updated throughout the day — social media links are at the bottom of this post.

After the rain moves out tonight, temperatures drop…we’ll end up in the 40s by early tomorrow morning:

Plenty of sunshine tomorrow, but temperatures will have to struggle to reach up to around 60°:

The cool weather will stick around most of next week — highs in the 50s and lows in the 30s will prevail through Wednesday, which happens to be the first day of spring:Thursday has a better chance of actually feeling like spring, as highs return to the 60s.



Erin Clanahan: Twitter & Facebook Instagram

Paul Heggen: Twitter & Facebook Instagram

Wes Hohenstein: Twitter & Facebook

Bill Reh: Twitter & Facebook

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